• Korean Journal of Microbiology
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• v.31 no.3
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• pp.224-229
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• 1993

GABA transminase (4-aminobutyrate aminotransferase), which catalyzes the breakdown of the major inhibitory neurotransmitter, GABA, in mammalian brain, was inactivated by preincubation with the mycotoxin patulin. The time course of the reaction was significantly affected by the substrate .alpha.-ketoglutarate, which aforded complete protection against the loss of catalytic activity. The recovery from the inhibition of patulin by the addition of dithiothreitol (DTT) supports that patulin reacts with the sulfhydryl residue in the catalytic domain of the enzyme. The reconstitution of the reduced enzyme and apoenzyme with pyridoxal-5-P(PLP) was inhibited by another mycotoxin, penicilic acid. This mycotoxin may interact with lysyl residue of the enzyme. Therefore, it is postulated that the critical sulfhydryl and lysyl residues in the catalytic domain of the enzyme react with mycotoxin patulin and penicillic acid, respectively.

• Archives of Pharmacal Research
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• v.19 no.6
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• pp.480-485
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• 1996

Brain GABA transaminase is inactivated by preincubation with antidepressant/antipanic drug pheneizine (${\beta}$ethylphenylhydrazine) (mixing molar ratio 10:1) at pH 7.4. The reaction of enzyme with phenelzine was monitored by absorption and fluorescence spectroscopic methods. The inactive enzyme was fully reconstituted by addition of cofactor pyridoxal-5-phosphate. This result implies that the blocking of 1 mol of pyridoxal-5-phosphate per enzyme dimer is needed for inactivation of the enzyme. The time course of the reaction is significantly affected by the substrate .alpha.-ketoglutarate, which afforded complete protection against the loss of catalytic activity. The kinetic studies shows that phenelzine reacts with the cofactor of enzyme with a second-order rate constant of $2.1{\times}10^3M^{-1}s^{-1}$. It is postulated that the antidepressant/antipanic drug phenelzine is able to elevate the neurotransmitter GABA levels in central nervous system by inhibitory action on GABA degradative enzyme GABA transaminase.